Buying a new 1TB hard drive and a 4gb RAM but now I'm stuck with the choice of which OS I should install. I could use Windows XP Pro with SP3 but now I'm curious about the difference between Vista 32-bit and 64-bit. I know 64-bit will make the most of the RAM and should in theory make it more powerful but last time I tried it on my laptop, it seemed to have a lot of problems trying to run some of the programs I used. So is the 64-bit worth it? Also, my current 2GB ram is a PC2-4200 and the new 4GB I ordered is a PC-6400. Even though combining the two should give me 6GB RAM, what are the problems of installing an older RAM with a lower spec with a newer RAM with a slightly higher spec?